The present invention relates to substrate processing. Specifically, the present invention relates to an apparatus and method for cleaning a chamber in a substrate processing system that is less destructive to the chamber walls and the components contained therein and increases the number of wafers that may be processed between wet cleans.
One of the primary steps in the fabrication of modern semiconductor devices is the formation of a layer, such as a metal silicide layer like tungsten silicide (WSix), on a substrate or wafer. As is well known, such a layer can be deposited by chemical vapor deposition (CVD). In a conventional thermal CVD process, reactive gases are supplied to the substrate surface where heat-induced chemical reactions take place to form the desired film over the surface of the substrate being processed. In a conventional plasma-enhanced CVD (PECVD) process, a controlled plasma is formed using radio frequency (RF) energy or microwave energy to decompose and/or energize reactive species in reactant gases to produce the desired film.
One problem that arises during such CVD processes is that unwanted deposition occurs in the processing chamber and leads to potentially high maintenance costs. With CVD of a desired film on a wafer, undesired film deposition can occur on any hot surface including the heater or process kit parts of the apparatus, because the reactive gases can diffuse everywhere, even between cracks and around corners, in the processing chamber. During subsequent wafer depositions, this excess growth on the heater and/or other parts of the apparatus will accelerate until a continuous metal silicide film is grown on the heater and/or these other parts. Over time, failure to clean the residue from the CVD apparatus often results in degraded, unreliable processes and defective wafers. When excess deposition starts to interfere with the CVD system's performance, the heater and other process kit parts (such as the shadow ring and gas distribution faceplate) can be removed and replaced to remove unwanted accumulations in the CVD system. Depending on which and how many parts need replacing and the frequency of the replacement, the cost of maintaining the substrate processing system can become very high.
In these CVD processes, a reactive plasma cleaning is regularly performed in situ in the processing chamber to remove the unwanted deposition material from the chamber walls, heater, and other process kit parts of the processing chamber. Commonly performed between deposition steps for every wafer or every n wafers, this cleaning procedure is performed as a standard chamber cleaning operation where the etching gas is used to remove or etch the unwanted deposited material. Common etching techniques include plasma CVD techniques that promote excitation and/or disassociation of the reactant gases by the application of RF energy with capacitively-coupled electrodes to a reaction zone proximate the substrate surface. In these techniques, a plasma of highly reactive species is created that reacts with and etches away the unwanted deposition material from the chamber walls and other areas. However, with some metal CVD processes, etching gases useful for etching unwanted metal are often corrosive and attack the materials which make up the chamber, heater, and process kit parts of the processing chamber.
Moreover, use of in situ plasma cleaning also causes ion bombardment of the metallic parts of the CVD apparatus. The ion bombardment makes difficult to effective cleaning of the excess CVD film without damaging the heater and other chamber parts in the cleaning process. Thus, maintaining chamber performance may result in a reduction of the operational life of these components. In addition to such in situ plasma cleaning procedures and occurring far less frequently, a second cleaning procedure involves opening the processing chamber and physically wiping the entire reactor—including the chamber walls, exhaust and other areas having accumulated residue—with a special cloth and cleaning liquids. This cleaning procedure is commonly referred to as a wet clean, due to the liquids employed. Failure to periodically employ a wet clean results in impurities accumulating in the CVD apparatus that which can migrate onto the wafer and cause device damage. Thus, properly cleaning CVD apparatus is important for the smooth operation of substrate processing, improved device yield and better product performance.
As an alternative to in situ plasma cleaning, other conventional CVD apparatus have a separate processing chamber connected to a remote microwave plasma system. Because the high breakdown efficiency with a microwave plasma results in a higher etch rate (on the order of about 2 μm/min) than is obtained with a capacitive RF plasma, these remote microwave plasma systems provide radicals from the remote plasma that can more gently, efficiently and adequately clean the residue without ion bombardment. Yet, the remote microwave plasma system suffers, although to a lesser degree, some of the drawbacks of an in situ plasma cleaning system. Some of the radicals from the remote plasma may react with the components of the chamber, etching the same. As discussed above, this may cause physical damage to the components of the chamber, including the chamber walls, substantially reducing the operational life of the same. In addition, the aforementioned reactions between the chamber components and the radicals leaves a residue on the chamber components which may contaminate wafer surfaces during processing.
What is needed, therefore, is a cleaning method and system for a CVD apparatus that is less destructive to the chamber walls and the components contained within the CVD chamber.